The present invention relates to a dot matrix printer, and more particularly to an impact type printing head for use in the dot matrix printer.
A printer of this kind has a plurality of selectively driven printing needles or printing wires for printing figures and letters in the form of dot matrixes on paper. Presently, most of the printers of this kind employ electromagnets for driving the printing needles or wires. For example, a line printer disclosed in U.S. Pat. No. 3,941,051 comprises plate springs each having a printing needle, permanent magnets disposed at the lower rear of the plate springs, and electromagnets at the upper rear of the plate springs. The plate springs are bent by the attracting magnetic force of the permanent magnet. When one of the electromagnets is energized, the magnetic force of the permanent magnet is offset, and the printing needle is projected toward a platen by the resilient force of the plate spring. However, this conventional printer requires an excessively large driving current due to the heat generated in the coil of the electromagnets, eddy currents and a hysteresis loss occurring in the yoke and armature. Therefore, the current capacity of a driving circuit for the electromagnets and the capacity of the power source are necessarily large. This causes the printer to be large and expensive. Furthermore, the use of electromagnets and permanent magnets attached to the reciprocating printing mechanism produces a heavy printing mechanism. Therefore, high printing speeds cannot easily be realized.